A 61-year-old woman comes to the physician for a follow-up examination 1 week after undergoing right-sided radical mastectomy and axillary lymph node dissection for breast cancer. She says that she has been unable to comb her hair with her right hand since the surgery. Physical examination shows shoulder asymmetry. She is unable to abduct her right arm above 90 degrees. When she pushes against a wall, there is protrusion of the medial aspect of the right scapula. Injury to which of the following nerves is the most likely cause of this patient's condition?

Upper trunk of the brachial plexus

A previously healthy 2-year-old boy is brought to the emergency room by his mother because of persistent crying and refusal to move his right arm. The episode began 30 minutes ago after the mother lifted him up by the arms. He appears distressed and is inconsolable. On examination, his right arm is held close to his body in a flexed and pronated position. Which of the following is the most likely diagnosis?

Supracondylar fracture of the humerus

A 4-year-old boy is brought to the pediatrician by his mother for a routine medical examination. His medical history is relevant for delayed gross motor milestones. The mother is concerned about a growth delay because both of his brothers were twice his size at this age. Physical examination reveals a well-groomed and healthy boy with a prominent forehead and short stature, in addition to shortened upper and lower extremities with a normal vertebral column. The patient’s vitals reveal: temperature 36.5°C (97.6°F); pulse 60/min; and respiratory rate 17/min and a normal intelligence quotient (IQ). A mutation in which of the following genes is the most likely cause underlying the patient’s condition?

Fibroblast growth factor receptor 3

Runt-related transcription factor 2

Insulin-like growth factor 1 receptor

A 42-year-old woman comes to the physician because of increasing pain in the right hip for 2 months. The pain is intermittent, presenting at the lateral side of the hip and radiating towards the thigh. It is aggravated while climbing stairs or lying on the right side. Two weeks ago, the patient was treated with a course of oral prednisone for exacerbation of asthma. Her current medications include formoterol-budesonide and albuterol inhalers. Vital signs are within normal limits. Examination shows tenderness to palpation over the upper lateral part of the right thigh. There is no swelling. The patient is placed in the left lateral decubitus position. Abducting the extended right leg against the physician's resistance reproduces the pain. The remainder of the examination shows no abnormalities. An x-ray of the pelvis shows no abnormalities. Which of the following is the most likely diagnosis?

Greater trochanteric pain syndrome

A 44-year-old woman comes to the physician for the evaluation of right knee pain for 1 week. The pain began after the patient twisted her knee during basketball practice. At the time of the injury, she felt a popping sensation and her knee became swollen over the next few hours. The pain is exacerbated by walking up or down stairs and worsens throughout the day. She also reports occasional locking of the knee. She has been taking acetaminophen during the past week, but the pain is worse today. Her mother has rheumatoid arthritis. The patient is 155 cm (4 ft 11 in) tall and weighs 75 kg (165 lb); BMI is 33 kg/m2. Vital signs are within normal limits. Examination shows effusion of the right knee; range of motion is limited by pain. There is medial joint line tenderness. Knee extension with rotation results in an audible snap. Further evaluation is most likely to show which of the following?

Hyperintense line in the meniscus on MRI

Trabecular loss in the proximal femur on x-ray

Posterior tibial translation on examination

Erosions and synovial hyperplasia on MRI

Anterior tibial translation on examination

Bones and joints of upper limb for USMLE Step 2 CK: High-Yield Anatomy Lessons

Shoulder Girdle & Humerus - The Bony Framework

Bones of the shoulder girdle: clavicle, scapula, humerus

Shoulder Girdle: Connects the upper limb to the axial skeleton. Includes the Clavicle & Scapula.
- Clavicle: S-shaped strut. Articulates with the sternum (sternoclavicular joint) & acromion (acromioclavicular joint). Common fracture site: junction of middle and lateral thirds.
- Scapula: Triangular bone with key landmarks: spine, acromion, coracoid process, & glenoid cavity.
Proximal Humerus:
- Head: Articulates with the glenoid.
- Surgical Neck: Inferior to the tubercles; a frequent fracture site.
⭐ Fracture of the surgical neck of the humerus places the axillary nerve and posterior circumflex humeral artery at risk of injury. 📌 Supraspinatus, Infraspinatus, Teres minor attach to the Greater Tubercle; Subscapularis attaches to the Lesser Tubercle.

Forearm Bones & Joints - The Dynamic Duo

Radius & Ulna: Parallel bones forming the forearm (antebrachium).
- Radius: Shorter, lateral bone; thumb side. Head articulates with capitulum of humerus.
- Ulna: Longer, medial bone; pinky side. Olecranon and trochlear notch articulate with trochlea of humerus.
- 📌 Mnemonic: CRAzy Thumb (Capitulum-Radius) and TRUe Love (Trochlea-Ulna).
Key Joints:
- Proximal & Distal Radioulnar Joints: Allow pronation and supination.
- Radiocarpal (Wrist) Joint: Radius articulates with scaphoid and lunate carpal bones.

Proximal Ulna and Radius Anatomy

⭐ Colles' Fracture: A fracture of the distal radius, often from falling on an outstretched hand (FOOSH). Results in a "dinner fork" deformity. Common in older adults with osteoporosis.

Wrist & Hand Bones - The Fine Manipulators

Carpal Bones (8): Two rows of four bones forming the wrist.
- 📌 Mnemonic: So Long To Pinky, Here Comes The Thumb.
- Proximal Row: Scaphoid, Lunate, Triquetrum, Pisiform.
- Distal Row: Trapezium, Trapezoid, Capitate, Hamate.
Metacarpals (5): Numbered I-V (thumb to little finger); connect carpals to phalanges.
Phalanges (14): Bones of the digits.
- Digits II-V have proximal, middle, and distal phalanges.
- Thumb (Pollex) has only proximal and distal phalanges.

⭐ Scaphoid Fracture: Most common carpal fracture (e.g., from a fall on an outstretched hand). Prone to avascular necrosis due to retrograde blood supply.

Bones of the Hand and Wrist

Clinical Correlates - High-Yield Injuries

Clavicle Fracture: Most common fracture, typically mid-third. Risk to brachial plexus & subclavian artery.
Humerus Fractures & Nerve Injury:
- Surgical Neck: Axillary n. → deltoid paralysis, loss of sensation over lateral shoulder.
- Mid-Shaft/Radial Groove: Radial n. → wrist drop, sensory loss on posterior forearm/hand.
- Supracondylar: Median n. & Brachial a. → risk of Volkmann's ischemic contracture.
Shoulder Dislocation: Axillary n. injury is common with anterior dislocations (most frequent type).
Distal Radius Fracture (Colles'): From fall on an outstretched hand (FOOSH). Leads to a "dinner fork" deformity.

⭐ Scaphoid Fracture: Also from FOOSH. Presents with anatomical snuffbox tenderness. High risk of avascular necrosis (AVN) due to retrograde blood supply. A normal initial X-ray does not rule out a fracture.

High‑Yield Points - ⚡ Biggest Takeaways

Scaphoid fractures, the most common carpal injury, carry a high risk of avascular necrosis due to retrograde blood supply.

Anterior shoulder dislocation is the most frequent type, often causing injury to the axillary nerve.

The supraspinatus is the most commonly torn rotator cuff muscle, often injured during abduction.

Colles' fracture of the distal radius presents with dorsal displacement, creating a "dinner fork" deformity.

A "Boxer's fracture" is a break in the neck of the 5th metacarpal.

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